Psychobiological approaches have revealed numerous examples of group differences among neuropsychiatric patients with intellectual disabilities. It is unclear, however, to what extent these differences are manifested behaviorally. In the past, methodological difficulties adapting complex neuropsychological paradigms to MR/DD populations have limited investigation. This project proposes to begin the process of overcoming these limitations. We suggest techniques to redress these problems, and will use them to assess specific group differences. Matched groups of subjects with autism and undifferentiated mental retardation will be administered tests that evaluate specific claims about autistic behavior. Within both the visual and auditory modalities, we will assess learning and generalization of simple and conditional discriminations, formation of equivalence classes both within and across modalities, immediate and delayed recall, the ability to shift and sustain attention, and several other behavioral measures. We have adapted stimulus control procedures developed in our laboratory to assemble a neurobehavioral test battery. We will use this battery to evaluate specific claims of behavioral pathology in autism, comparing autistic individuals with a contrast group of subjects with undifferentiated mental retardation. We will test whether or not autistic subjects have comparatively more (i) perseveration and behavioral rigidity, (ii) restricted stimulus control (overselectivity), (iii) attentional deficits, (iv) memory deficits, (v) deficient affective comprehension, and (vi) symbolic processing abnormalities. This undertaking will provide an initial attempt to determine whether diagnosis must be considered when designing teaching interventions for individuals in the low range of intellectual function. It can be seen as a first step in developing a more comprehensive neurobehavioral assessment battery for this group.